Process for the production of saturated aliphatic nitro compounds



I PROCESS FOR THE PRODUCTION OF SATURATED ALIPHATIC NITRO COMPOUNDS Charles Philip Spaeth, Woodhury, N.J., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware I No Drawing. Application April 16, 1957 Serial No. 653,072

8 Claims. (Cl. 260-644) The present invention relates to a process for the preparation of nitro derivatives of alkanes, cycloalkanes, and aryl-substitutedalkanes. More particularly, the present invention relates to a process for the liquid-phase nitration of alkanes, cycloalkanes, and aryl-substituted alkanes by nitricoxide.

Nitro derivatives of such hydrocarbons are useful as solvents and as chemical intermediates, particularly as intermediates for valuable amines. Heretofore, the nitro derivatives were prepared generally by processes involvingthe use of nitric acid and/or nitrogen dioxide as the nitrating agent. These nitrating agents,-however, have not been entirely satisfactory from the viewpoint of economics and safety. Not only does the corrosive action of these agents necessitate the use of expensive chrome-steel or glass-lined storage and handling equipment, but also in'most nitrations by nitric acid or nitrogen dioxide, large amounts of undesirable oxidation products are formed. In addition to the economic disadvantages incurred by the use of nitric acid or nitrogen di-' oxide, the use of these nitrating agents requires careful control of reaction conditions to prevent the formation of unstable and consequently hazardous reaction mixtures. Furthermore, in the nitric acid processes of the prior art the substitution of the nitro group cannot be limited solely to the alkyl side-chain of an aryl-substituted alkane; in these processes, the nitro substituent also is introduced on the aromatic ring, giving undesirable byproducts and lower yields of the desired products.

Accordingly, an object of the present invention is to provide a simple and economical process for the nitration of alkanes, cycloalkanes, and aryl-substituted alkanes to give nitro compounds unaccompanied by large amounts of by-products. A further object of the present invention is to provide an inherently safe process for the nitration of hydrocarbons. A still further object of the present invention is to provide a nitration process whereby nitro substituents can be introduced readily into the alkyl side-chain of aryl-substituted alkanes without attendant ring nitration.

I have found that the foregoing objects may be achieved when I react nitric oxide and an alkane, cycloalkane, or aryl-substituted alkane in the liquid phase at a temperature within the range of 160 and 300 C.

In accordance with the process of the present invention, nitric oxide is bubbled through an alkane, cycloalkane, or aryl-substituted alkane in a reaction zone maintained at a temperature within the range of 160-300 C. and at a pressure within the range of 125-600 p.s.i.ga., the hydrocarbon being maintained substantially in the liquid phase.

2,883,432 Patented Apr. 21, 1959 The following examples serve to illustrate specific embodiments of the method of carrying out the process of the present invention. However, they Will be understood to be illustrative only and not as limiting the invention in any manner. The parts in the examples are parts by weight.

Example 1 Cyclohexane in the amount of 1008 parts was introduced into an autoclave which had previously been flushed with nitrogen. The cyclohexane was heated to 190 C., and the pressure was adjusted to 300 p.s.i.ga. with nitrogen. Nitric oxide at the rate of about 3 parts per min ute was introduced below the surface of the cyclohexane for 20 minutes, the temperature and pressure being maintained at the initial levels. After the addition of nitric oxide was complete, the reaction mixture was cooled to 30 C., and then the autoclave was vented. The product mixture was removed, Washed with dilute sodium bicarbonate solution, dried over anhydrous magnesium sulfate, and then analyzed. The analysis indicated that nitrocyclohexane in a conversion of 70.5% was obtained. The analysis also showed that cyclohexyl nitrite, carbonyl compounds, andcarboxy compounds in conversions of 4.5,-9.8. and 1.0%, respectively, also were obtained.

Example 2 The procedure of Example 1 was repeated, with the exception that the time of addition of the nitric oxide was minutes. Analysis of the product mixture showed that nitro-cyclohexane was obtained in 60% conversion, and cyclohexyl nitrite and carbonyl and carboxy compounds were obtained in 1.8- and 7% conversions, respectively. I

Example 3 Cyclohexane (860 parts) was treated with nitric oxide in the manner described in Example 1. The nitric oxide was introduced at the rate of about 4 parts per minute the procedure of Example 1, a mole ratio of n-nonane to nitric oxide of 7/5 being used. The reaction was effected at 190 C. and 300 p.s.i.ga. for a reaction period of 20 minutes. Analysis of the product mixture showed that a mixture of primary and secondary mononitrononanes in 71% conversion was obtained.

Example 5 In the experiments summarized in the following table, various hydrocarbons were treated with nitric oxide in the manner described in Example 1. The following conditions were used: nitric oxide feed rate, 3 parts per minuteg time of nitric oxide addition, 20 minutes; temperature, 190200 C.; and pressure, 300 p.s.i.ga. The prod- I ucts obtained are listed in the table.

, Amt. of OtherProduets (PercentOonv.)

Hydro- I Conv. Experiment Hydrocarbon carbon Nltro Derivatives (per- (parts) cent) Nltrltes Carbonyl Oarboxy Gompds. Compds.

A p-xylene j 1, 272 a-nltro-p-xylene 63 5. 5 18 3 B methylcyclohexaneu 882 l-methyl-l-nitroeyclohexane.-- 23 4. 7 9 1.3

sec-nitro deriv 30 1,3-d1methylcyclo- 1, 1,3-dimethyl-1-nitroeyclohexana 43 2. 7 9. 5 2

hexane. sec-nitro deriv 13 As may be seen by reference to the foregoing examples, the nitration process of the present invention proceeds smoothly and rapidly to give nitro compounds as the major product without the formation of appreciable quantities of undesired oxidation products. The nitration can be effected at temperatures of at least 160 C., and good results are obtained at temperatures of up to about 300 C. At higher temperatures tars are .formed and yields are correspondingly decreased.

Pressure is applied to the reaction system in order to maintain the hydrocarbon substantially in the liquid phase. The exact pressure applied, therefore, is dependent upon the temperature maintained in the reaction zone. Generally, the reactor will be pressurized to about 125-600 p.s.i. ga., a minimum pressure of 125 p.s.i. ga. usually being requiredto maintain the liquid phase at the temperatures used in the process. At pressures above 600 p.s.i. ga., difficulties are. encountered in operating the process due to the effect of such pressures on nitric oxide. The reactor can be pressurized with any inert gas, in as much as the specific inert gas used is not critical. In addition to the nitrogen and helium exemplified, carbon dioxide also can be used. Inert gaseous diluents may also be used.to dilute the nitric oxide feed and, thereby, moderate the reaction.

The rate of introduction of the nitric oxide is governed bythe rate at which it reacts with the hydrocarbon which in turn depends on pressure and temperature and the hydrocarbon used. The reaction time and ratio of reactantshave been varied widely without serious effects on the amount of nitro hydrocarbon formed. When, as shown by the examples, the hydrocarbon is present in excess, the unreacted hydrocarbon simply is recovered and recycled. Excess nitric oxide, which is not absorbed in the hydrocarbon, likewise is not deleterious to the carrying out of the present process and can be recovered and reused. The nitric oxide constitutes the nitrating agent of the present invention, and, as such, nitric oxide substantially free of other oxides of nitrogen, i.e., containing only minor amounts, about 1 or 2% of the other nitrogen oxides, is used in carrying out the process of the present invention.

The process of the present invention is general for alkanes, cycloalkanes, and aryl-substituted alkanes which can be maintained in the liquid phase under the reaction conditions. In addition to the hydrocarbons used in the experiments described in the foregoing examples, various other hydrocarbons can be nitrated by the process of the present invention. For example, additional nitro parafiins can be prepared readily from the corresponding paraflinic hydrocarbons, e.g., n-hexane, neohexane, isooctane, and n-decane. Other cycloalkanes which can be nitrated by the present process include, among others, cycloheptane and cyclopentane. The term cycloalkane as used throughout the specification and claims also includes, of course, alkyl-substituted cycloalkanes such as the exemplified methylcyclohexane and dimethylcyclohexane and others, e.g., alkylated cycloheptanes and cyclopentanes. Additional aryl-substituted alkanes suitable for use in the process of the present invention are, for example, cumene, cymene, durene, toluene, and ethylbenzene. Furthermore, nonhydrocarbon substituents, such as nitro or halo groups, present on the hydrocarbons to be nitrated do not interfere in the carrying out of the process of the present invention, and compounds such-as nitro-cyclohexane, chlorodecane, bromopentane, etc. constitute suitable starting materials. Of course, when a nitro-substituted hydrocarbon is used as the starting material, a polynitro derivative is obtained which containsan additional nitro group.

Although the preceding examples illustrate the process as a batchwise process, equally feasible is the carrying out of the process in a continuous manner. For example, nitric oxide and the hydrocarbon may be introduced continuously into a reaction zone maintained at the desired operating conditions, while the product mixture is continuously withdrawn.

The invention has been described in detail in the fOI'C'. going. It will be apparent to those skilled in the art that many variations are possible without departure from the scope of the invention. For example, the hydrocarbon may be admixed with a diluent, e.g., benzene or acetonitrile, which is inert to the nitric oxide under the reaction conditions. I intend, therefore, to be limited only by the following claims.

I claim:

1. A process for the preparation of aliphatic nitro derivatives of alkane, cycloalkane, and the simpler mononuclear aryl-substituted alkane hydrocarbons which comprises introducing nitric oxide into said hydrocarbons in a reaction zone maintained at a temperaturewithin the range of 160 and 300 C. and at a pressure within the range of and 600 p.s.i.ga., said hydrocarbons being maintained substantially in the liquid phase.

2. Process according to claim 1, wherein the reactor is pressurized with an inert gas selected from the group consisting of nitrogen, helium, and carbon dioxide.

3. Process according to claim 1, wherein the hydrocarbon is present in excess.

4. Process for the preparation I of nitrocyclohexane which comprises introducing nitric oxide into cyclohexane in a reaction zone maintained at a temperature Within the range of and 300 C. and at a pressure within the range of 125 and 600 p.s.i.ga., said cyclohexane being maintained substantially in the liquid phase.

5. Process for the preparation of a-nitro-p-xylene which comprises introducing nitric oxide into p-xylene in a reaction zone maintained at a temperature within the range of 160 and 300 C. and at a pressure within the range of 125 and 600 p.s.i.ga., said p-xylene being maintained substantially in the liquid phase.

6. Process for the preparation of nitro derivatives of -methylcyclohexane which comprises introducing nitric oxide into methylcyclohexane in a reaction zone maintained at a temperature within the range of 160 and 300 C. and at a pressure within the range of 125 and 600 p.s.i.ga., said methylcyclohexane being maintained substantially in the liquid phase.

7. Process for the preparation of nitro derivatives of dimethylcyclohexane which comprises introducing nitric oxide into dimethylcyclohexane in a reaction zone maintained at a temperaturewithin the range of 160 and 300 C. and at a pressure within the range of 125 and 600 p.s.i.ga., said dimethylcyclohexane being maintained substantially in the liquid phase.

8. Process for the preparation of nitro derivatives of nnonane which comprises introducing nitric oxide into nnonane in a reaction zone maintained at a temperature within the range of 160 and 300 C. and at a pressure within the range of 125 and 600 p.s.i.ga., said n-nonane being maintained substantially in the liquid phase.

References Cited in the tile of this patent UNITED STATES PATENTS 2,459,690 Doumani et al. Jan. 18, 1949 2,511,454 Bishop June 13, 1950 2,597,698 Bachmann et al May 20, 1952 2,609,401 Hass et al. Sept. 2, 1952 OTHER REFERENCES Bachmann eta1.: Journal of Organic Chemistry, vol. 17, pages 906-13 (1952). 

1. A PROCESS FOR THE PREPARATION OF ALIPHATIC NITRO DERIVATIVES OF ALKANE, CYCLOALKANE, AND THE SIMPLER MONONUCLEAR ARYL-SUBSTITUTED ALKANE HYDROCARBONS WHICH COMPRISES INTRODUCING NITRIC OXIDE INTO SAID HYDROCARBONS IN A REACTION ZONE MAINTAINED AT A TEMPERATURE WITHIN THE RANGE OF 160* AND 300* C. AND AT A PRESSURE WITHIN THE RANGE 125 AND 600 P.S.I.GA., SAID HYDROCARBONS BEING MAINTAINED SUBSTANTIALLY IN THE LIQUID PHASE. 